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posted by The Bangkok Consultant
Recommended: Using your mobile in Thailand
There are two main river boat taxis you need to know about. There is the Chao Phraya Express, which you will see most Thai people using. Central Pier (Saphan Taksin BTS) can be a little confusing when figuring out which boat to get, but just follow the mass of Thais. Most other piers are usually straightforward. The express boat costs a flat-rate of 14 baht and should come around every 10-20 minutes, stopping at the main piers of interest.
Another convenient option is the tourist boat costing 40 baht. During the journey, someone will offer some information in English over a loud speaker, and will tell you what can be seen at each of the stops. On hot days, it's sometimes better just to use these rather than wait for an express boat, but it's up to you.
At Central Pier, someone will inevitably try and persuade you to use the tourist ferry for 100 baht, which should take you directly to Rattanakosin, but I wouldn't bother. Don't be led by anyone offering you help because they will put you on a more expensive boat.
Don't buy tickets at the piers, even if people insist. It's all bollocks. After a couple of trips, you'll know it like the back of your hand. You may end up going in the wrong direction, to begin with, but hey you're on holiday so who cares? You never know, you may find something unexpected. Google Maps can help with this.
Other, select, boats stop off at specific hotels, so ask at your hotel if this applies to you.